It is known that tablets, especially tablets for pharmaceutical use, are currently made by machines known as tablet presses which work by compressing a powdered or granular substance or product.
One prior art tablet press substantially comprises a feed hopper that contains and feeds the powdered or granular substance to a turret consisting of a first rotary disc having uniformly distributed around its edge a plurality of seats or matrices for volumetrically dosing and forming the tablets.
The tablets are formed by oppositely reciprocating punches uniformly distributed around two further discs forming part of said turret. These two further discs are located above and below the first disc and rotate continuously about the axis of the first disc and in synchrony with the latter.
The two punches in each pair—one above and one below—access a single matrix simultaneously and compress the dose of product inside the matrix with a predetermined force that gradually increases as the discs rotate and until a tablet is formed.
The tablet press therefore has a precise angular position where the powdered or granular product is loaded into the forming seats or matrices; another position where the product is compressed and yet another position, close to the first, where the formed tablets are fed out towards an outfeed chute: in practice, the tablet is formed in one complete rotation of the aforementioned discs.
The tablet presses of the type described above, usually with high-output features (hence, typically not for laboratory use) may also be used for research or experimental purposes, for example to test tablets made with a new powdered product.
To do this, a limited quantity of the powdered product to be tested is fed into the tablet press. Before this is done (since the machine has to work with a partial load), some of the operating stations of the compression turret, within a defined arc of the rotary discs, are inhibited so that they do not produce any tablets.
In other words, the pairs of punches of the seats or matrices to be inhibited are physically removed from the rotary discs, together with all the mechanical parts that allow their reciprocating motion.
In addition, the powder feed channels leading to the inhibited compression seats are sealed using suitable plugs.
With the turret set up in this way, therefore, there are operating units capable of making tablets for experimental purposes on only a limited angular sector of the machine, whilst the rest of the turret continues to rotate at the usual angular speeds but without producing any tablets since the operating elements have been removed.
This particular set-up, however, may lead to problems.
Indeed, removal and reassembly of the operating units is a slow and laborious task which, in high-output machines, is a serious drawback. Also, removing the punches from the operating stations to be inhibited creates the risk of unwanted materials such as lubricating oil or grease penetrating the stations that remain operative owing to leaks caused by imperfect seals of the elements used to plug the inhibited parts. This in turn leads to contamination which is likely to invalidate the test being carried out. Another serious problem is the uneven distribution of forces during the test because, during rotation of the turret, the punches remaining on the single operating sector of the turret exert forces that are not counterbalanced at the inhibited stations of the remaining sector from which the punches have been removed.
This may damage the active punches-and produce a test result that is ineffectual for the purposes of tablet production with the tested powder.
The present invention therefore has for an object to overcome the above mentioned disadvantages by providing a tablet press machine that can be quickly and effectively adapted to produce tablets for research and experimental purposes at only some of its operating stations, while maintaining a balanced distribution of forces at all the stations of the turret, including the inoperative stations.